Method and device for the producing of a gas rich in hydrogen by thermal pyrolysis of hydrocarbons

ABSTRACT

The invention concerns a method for producing a gas rich in hydrogen by thermal pyrolysis of hydrocarbons which consists in carrying out, in a reactor (R) a catalyst-free thermal cracking to pyrolyze a fuel selected so as to produce either a gas rich in hydrogen and free of carbon monoxide, or a gas rich in hydrogen and containing carbon monoxide and in using said gas effluents during pyrolysis and inert with respect to the cell as fuel at the burner (B) to heat the reactor so as to bring it to a reaction temperature, and which consists, subsequently, in burning the powder carbon produced in the reactor (R) during the pyrolysis reaction either to produce carbon monoxide or to produce carbon dioxide. The invention is useful in particular for supplying hydrogen to fuel cells and for producing synthesis gas.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention involves a method for the pyrolysis of hydrocarbonsor oxygenised fuels (alcohol, ETB, MTB, . . . ) for the production of ahydrogen-rich gas and possibly for certain applications of carbonmonoxide (CO). In particular, but not exclusively, it applies to theconversion of a fuel into a hydrogen-rich gas for fuel cells either lowtemperature cells of the proton exchange membrane type (PEM) or hightemperature cells or molten carbonate fuel cells (MCFC) or solid oxidefuel cells (SOFC).

[0003] The expression <<net calorific value>> or NCV is hereafterdefined. The calorific value is defined as the quantity of heat givenoff by the full combustion of the unit of fuel considered. The netcalorific value excludes the heat given off, the water condensation heatremaining in vapour state at the end of combustion.

[0004] 2. Description of the Prior Art

[0005] In general, fuel cells are known to be electrochemical systemsdirectly converting chemical energy into electrical energy. Thetheoretical yield is very high and the sub-products pollute very little.In addition, originally in space missions, fuel cells have demonstratedtheir efficacy, reliability and longevity. These qualities confirm thevalue of fuel cells in the production of portable electricity (severalhundred watts to several kilowatts) or permanent or on board electricity(2 kilowatts to 200 kilowatts). Therefore, fuel cells represent apossible alternative to thermal engines in a great many of their uses.They can also be used in the creation of co-generation boilers.

[0006] Hydrogen fuel may come from a pressurised or cryogenic tank.However, given the safety problems involved in the storage of hydrogen,it is sensible to obtain it from a fuel (hydrocarbon or alcohol) wherethe hydrogen is released along when needed.

[0007] For this purpose, different chemical reactions may be used:vaporeforming, partial oxidation and pyrolysis. Each of these reactionscan be activated thermally and/or by means of a catalyst.

[0008] The pyrolysis of hydrocarbons not only releases hydrogen but alsocarbon and other products with a considerable calorific value. Thismeans that the production of hydrogen by pyrolysis only has a sufficientyield if the energy content of the carbon and other co-products isvalorised. This situation differs from that of vaporeforming since thismethod releases the hydrogen contained in the fuel as well as thehydrogen contained in the water. The same is true of partial oxidationwhen it is coupled with a shift stage.

[0009] The reactions are: Vaporeforming: C₃H₈ + 6 H₂O → 3 CO₂ + 10 H₂Partial oxidation + C₃H₈ + 3/2 O₂ → 3 CO + 4 H₂ shift: CO + H₂O → CO₂ +H₂ (× 3) Pyrolysis: C₃H₈ + 3/2 O₂ + 3 H₂O → 3 CO₂ + 7 H₂ C₃H₈ → 3 C + 4H₂

[0010] However, the experiments carried out with these different methodsshow that the formation of non negligible quantities of carbon monoxideis inevitable as soon as the oxygen is introduced either directly or inwater vapour form.

[0011] Therefore, the reformers using partial oxidation or vaporeforminggenerally include a high or low temperature <<shift>> unit (COrecycling), a vapour generator and a drying unit to remove excessvapour. The conversion of CO is thereby difficult, expensive andcumbersome.

[0012] The invention begins with the finding that pyrolysis can be usedto eliminate these stages since it occurs without any source of oxygenthereby preventing the formation of CO. In addition, the partialpressure of hydrogen in the gas formed is comparatively higher than inthe other methods given, for example, the absence of nitrogen comingfrom the air used in partial oxidation.

[0013] In order to use the advantages of the method related to theabsence of oxygen molecules, the choice fuel is a hydrocarbon (methane,propane, butane) or a blend of hydrocarbons. However, an alcohol may beconsidered as choice in cases where the production of synthesis gases,mixtures of H2 and CO, is required.

[0014] Different methods for the use of pyrolysis reactions ofhydrocarbons have been recommended by several authors.

[0015] In U.S. Pat. No. 5,899,175, Manikowski et al. recommend a hybridsystem consisting of a catalytic pyrolysis reactor producing ahydrogen-rich gas and a blend of fuel residues. The hydrogen-rich gassupplies a fuel cell to produce electricity and the blend of fuelresidues is burned in a combustion engine to produce mechanical power.

[0016] This method allows for the processing of different liquid fuelsderived from petroleum. These fuels may be linear or branched alcaneswith at least five carbon atoms as well as all types of commercial fuelssuch gas, kerosene, . . .

[0017] The operating conditions chosen as such that only 20% of thehydrogen contained in the fuel is converted into di-hydrogen form.

[0018] Poirier et al. recommend a pyrolysis method producing thecatalytic decomposition of natural gas into a hydrogen-rich gas andcarbon (M. G. Poirier, C. Sapundzhiev, Catalytic decomposition ofnatural gas to hydrogen for fuel cell applications, Int. J. HydrogenEnergy, vol. 22, N^(o) 4, 1997, 429-433). The authors suggest the use ofhydrogen-rich gas to supply a PEM fuel cell. The catalytic bed on whichthe carbon formed during the pyrolysis reaction is deposited is thenregenerated by burning the carbon with air. In order to operate in asteady state in spite of the alternate sequences of pyrolysis andregeneration of the catalytic bed, the authors recommend a concept basedon the use of two alternating reactors. The first one operates inpyrolysis conditions to produce a hydrogen-rich gas while the secondregenerates the catalytic bed by oxidation of the carbon. The structureof the catalytic bed is organised to leave a sufficient dead volume toallow for the accumulation of a large quantity of carbon.

[0019] It should be noted that 45% of the net calorific value (NCV) ofthe natural gas remains in the carbon. Moreover, the pyrolysis ofmethane, the main component in natural gas, is endothermic and requiresabout 12% of the NCV of the natural gas. The authors therefore recommendthe use of the energy released by the combustion of the carbon toprovide the heat required for the decomposition of the natural gas.

[0020] In addition, it is necessary to mention that the catalytic bedproduces secondary parasite reactions. In fact, the production of CO isobserved during the pyrolysis phase while there is no oxygen supply.This emission probably is due to the partial reduction of oxides presentin the catalyst and formed during the regeneration phase.

[0021] Now, it we want to supply a PEM fuel cell with the hydrogen-richgas produced by this system, it is necessary to eliminate the CO sinceover 10 ppm of CO prevents the operation of the cell, since the anodecatalyst made of platinum contained is very sensitive to this pollutant.This purification may be carried out by a catalytic methanation method.A methanation reactor therefore has to be placed upstream from the PEMfuel cell on its hydrogen supply circuit.

[0022] A system of propane pyrolysis very similar to that of Poirier etal. was recommended by the German Ledjeff-Hey team. It mainly differs bythe type of hydrocarbon processed (K. Ledjeff-Hey, V. Formanski, Th.Kalk, J. Roes; Compact Hydrogen Production Systems for Solid PolymerFuel Cells, J. Power Sources, 71, 1998, 199-207) (K. Ledjeff-Hey, Th.Kalk, J. Roes; Catalytic cracking of propane for hydrogen production forPEM fuel cells, 1998 Fuel Cell Seminar, Palm Springs, Calif. 1998).

[0023] The pyrolysis reactions described above present serious defectsand deficiencies.

[0024] 1) In the energy balances:

[0025] In fact, pyrolysis methods reveal an intrinsic difficulty: thenet calorific value (NCV) of the hydrogen produced is generally of thesame magnitude, or even lower than that of the carbon and otherpyrolysis residues. There is a resultant problem in the management andvalorisation of the energy available in the carbon and other pryolysisresidues. If this problem is not suitably dealt with, the global energybalance of the system can only be very low and therefore unacceptable.

[0026] 2) In the sources of energy required for pyrolysis:

[0027] The heat available to heat and decompose the fuel within thepyrolysis reactor may come from three different sources:

[0028] the combustion of the carbon during the regeneration sequence,

[0029] the combustion of other pyrolysis residues,

[0030] the combustion of non-burnt gases leaving the fuel cell.

[0031] These three combustions take place within different chambers: theoxidation of solid carbon takes place inside the reactor in regenerationphase. The combustion of gas emissions may take place in a combustionchamber. It is therefore necessary to plan for very efficient heatexchange structures to provide the efficacy of the heat transfer betweenthe three reaction chambers: reactor during pyrolysis, reactor duringregeneration and burner.

[0032] 3) In the catalyst:

[0033] The use of catalytic beds in the two reactors (pyrolysis andregeneration) raises a great many problems: reduced efficacy and ageingof the catalyst, thermal inertia of the reactor, generation of CO duringthe pyrolysis phase, cost of the system, . . .

[0034] 4) In the uses:

[0035] The supra systems described were designed for the followingapplications:

[0036] hybrid generation of electricity by means of a fuel cell andmechanical energy by means of a combustion engine (U.S. Pat. No.5,899,175),

[0037] generation of electricity in a fuel cell (M. G. Poirier, C.Sapundzhiev, Catalytic decomposition of natural gas to hydrogen for fuelcell applications, Int. J. Hydrogen Energy, vol. 22, N^(o) 4, 1997,429-433), (K. Ledjeff-Hey, V. Formanski, Th. Kalk, J. Roes; CompactHydrogen Production Systems for Solid Polymer Fuel Cells, J. PowerSources, 71, 1998, 199-207), (K. Ledjeff-Hey, Th. Kalk, J. Roes,Catalytic cracking of propane for hydrogen production for PEM fuelcells, 1998 Fuel Cell Seminar, Palm Springs, Calif. 1998).

OBJECT OF THE INVENTION

[0038] The object of the invention is to eliminate these disadvantages.For this purpose, it recommends a solution that enables the use ofpyrolysis mechanisms for other applications such as:

[0039] Pre-reforming for high temperature melted carbonate fuel cells(MCFC) and solid oxide fuel cells (SOFC).

[0040] The co-generation of heat and electricity for the home either bycoupling with a PEM fuel cell or by coupling with a SOFC fuel cell.

[0041] The production of synthesis gas for petrochemistry.

SUMMARY OF THE INVENTION

[0042] To achieve these results, it recommends a method for theproduction of a hydrogen-rich gas that can be used in a fuel cell. Thismethod consists of carrying out thermal cracking in a reactor withoutcatalyst to pyrolyse a fuel chosen so as to produce either a gas rich inhydrogen and free of carbon monoxide or a gas rich in hydrogencontaining carbon monoxide. The gasses emitted during the pyrolysisreaction and inert with respect to the cell are used as fuel in theburner to provide the heating of the reactor in order to bring it to thereaction temperature.

[0043] Advantageously, the pulverulent carbon produced during thepyrolysis reaction may be burned so as to produce carbon monoxide or CO,at least in part, or to produce carbon dioxide or CO₂ (heat) to completethe heating of the reactions and possibly ensure a connected system ofheating.

[0044] According to another characteristic of the invention, the reactormay include two or more pyrolysis chambers used alternatively. In thiscase, the chamber not used for the pyrolysis is regenerated by theintroduction of air that, at the proper temperature, provokes thecombustion of the carbon deposited during the pyrolysis phase.

[0045] According to other characteristics of the invention:

[0046] The combustion chamber is placed at the core of the reactor orreactors;

[0047] The composition and type of blend supplying the burner vary intime;

[0048] The triggering of the combustion reactions in the burner takesplace by means of a plasma;

[0049] Effective heat exchange structures between the burner and thepyrolysis chamber are foreseen;

[0050] The catalytic bed is eliminated;

[0051] The hydrogen may be extracted and purified by means of apermeable and selective membrane for hydrogen;

[0052] The trapping of solid carbon particles in the pyrolysis reactoroccurs by means of filters made of refractory materials;

[0053] The production of pulverulent carbon becomes an advantage;

[0054] The pyrolysis reactions are catalysed by means of a plasma.

[0055] The combustion chamber is placed at the centre of the reactor orreactors in order to effectively heat the reactive mixture at hightemperature.

[0056] The composition and type of mixture supplying the burner varywith time. In fact, the triggering occurs with the fuel used for thepyrolysis. Once pyrolysis begins, the resulting co-products will berecycled to maintain the reaction in the burner. The carbon monoxideproduced during the combustion of the pulverulent carbon may also supplythe burner.

[0057] A device is foreseen to trigger the combustion in the burner bymeans of a plasma. Other means of production of the plasma are possible.The most simple method consists of the generation of sparks between theelectrodes of a spark plug similar to those used in car engines. Asystem of starting is required during the triggering of the combustionin the burner. This system may be stopped in a stationary state as soonas the temperature of the burner reaches a value enabling theself-ignition of the fuel blend.

[0058] Effective structures for heat transfer between the burner andpyrolysis chamber are foreseen. First, it is necessary to ensureexcellent heat transfer between the hot gases resulting from thecombustion in the burner and the wall of the burner. This transfer ismade more effective here by an increase in the contact surface of themetal with the hot gases by means of a metal structure. In particular,but not exclusively, it has the form of small wings, honeycomb or foam.This structure is placed inside the burner and the contact with theinner walls of the latter minimises the thermal resistance at thislevel.

[0059] In addition, the heat transfer between the burner chamber and thereactive gas circulating inside the pyrolysis reactor is optimised bymeans of a metal structure similar to the previous one, but in contactwith the outer wall of the burner.

[0060] Several disadvantages have been noted due to the presence of thecatalytic bed in the pyrolysis reactor. Work carried out in thelaboratory by the applicant demonstrated that, in a great many cases,the use of a catalyst was not required to improve the yield of thereaction. The elimination of the catalytic bed simplifies the systemwithout reducing the efficacy, reduces its cost and minimises theparasite uncontrolled production of CO.

[0061] An optional mode for the use of the method consists of extractingthe hydrogen from the reactor by means of membranes permeable andselective for hydrogen. In addition to the value of producing very purehydrogen, this mode increases the yield of the method since theextraction of the hydrogen shifts the chemical balance in the directionof a more complete reaction. Several ways of introducinghydrogen-selective permeable membranes permeable are described in theinfra text.

[0062] The dehydrogenation reactions considered lead to the productionof solid pulverulent carbon. In order to avoid the deposit of carbon inthe pipes of the hydrogen circuit and valorise this carbon by oxidationreactions, it is necessary to trap the solid carbon particles by meansof a filter placed inside the pyrolysis reactor. The filter consists ofa porous refractive material. One possible way to produce this filter isto form a buffer consisting of refractive fibres in, for example,aluminium wool.

[0063] The production of pulverulent carbon turns out to be an advantagehere. In fact, several options can be considered for its valorisation.For example, it may, in small stations, be collected for use as is inthe industry. It may also be oxidised in situ so as to form a source ofheat via the production of carbon dioxide or electricity via theproduction of carbon monoxide.

[0064] The production of carbon dioxide occurs through the combustionreaction:

C+O₂→CO₂

ΔH₂₉₈=−393.51 kJ

[0065] The production of carbon monoxide occurs by controlled oxidation,that is:

C+½O₂→CO

ΔH₂₉₈=−110.53 kJ

[0066] The CO produced can then be used as a fuel in a SOFC fuel cell,thereby increasing the yield in electricity.

[0067] As an option, a plasma generator may be incorporated in thepyrolysis reactor. In fact, the plasma induces very chemically reactiveradicals and plays a role similar to that of a catalyst. This effect, inparticular, results in the acceleration of the dehydrogenation reactionsof different hydrocarbons. Several types of plasma generators can beused for this application, mainly “barrier” discharge and micro-wavedischarge generators. Such devices have been described in former patentWO 98/28223.

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Means of production will be described below by way of nonlimiting examples, with reference to the appended diagrams in which:

[0069]FIG. 1 is a pyrolysis device according to the invention intendedfor the supply of a low temperature PEM fuel cell;

[0070]FIG. 2 represents a pyrolysis device according to the inventionintended for the supply of a high temperature SOFC fuel cell;

[0071]FIG. 3 represents a device including two reactors;

[0072]FIG. 4 represents a full circuit incorporating the device in FIG.3;

[0073]FIG. 5 represents a device using a polymer membrane operating atlow temperature intended for the purification of the H₂ rich blendobtained;

[0074]FIG. 6 represents a device using a metal membrane operating athigh temperature intended for the purification of the H₂ rich blendobtained;

[0075]FIG. 7 represents a device characterised by the fact that themetal membrane is placed inside the pyrolysis reactor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0076]FIG. 1 represents an example of a pyrolysis device according tothe invention. This device here feeds a low temperature PEM fuel cell 1.In its most simple form, this device comprises a single cylindricalreactor R heated by a cylindrical burner B incorporated at the centre soas to provide excellent heat transfer. The reactor-burner unit is placedin a cylindrical heat insulated sheath 2 intended to limit the heatlosses of the system. Reactor R is defined by the cylindrical wall ofthe burner and by an outer cylindrical wall coaxial to the burner. It isenclosed by a spherical cup-shaped bottom FD and by a ring-shaped top DAlocated around the top of the burner.

[0077] In this configuration, the pyrolysis reactor functionscyclically. It is in turn the seat of pyrolysis reactions that produce ahydrogen-rich gas and carbon oxidation reactions that regenerate thereactor.

[0078] To supply a PEM fuel cell, it is necessary to avoid introducingCO in the hydrogen-rich gas. As a result, for this application, thepyrolysis of an oxygenised fuel (alcohol, ETB, MTB, . . . ) will beavoided in favour of a hydrocarbon such as methane or propane.

[0079] Concerning the pyrolysis phase, reactor R is heated by means of aburner B at a temperature enabling cracking reactions of the hydrocarbonused. This temperature is in the neighbourhood of 550-650° C. forpropane and 700-800° C. for methane. The fuel, after eventualdesulfonation, is introduced in reactor R through duct 3 located at thetop of reactor R. The cracking by pyrolysis creates a hydrogen-rich gasand solid pulverulent carbon that is deposited in reactor R. Filter 4made of aluminium wool, located at the back of reactor R, retains thecarbon particles in the reactor and eliminates them from thehydrogen-rich gas extracted by duct 5 located on the other side offilter 4. Before introduction in the anode compartment of fuel cell 1,the hydrogen-rich gas is cooled by means of heat exchanger 6, at atemperature compatible with this type of cell, or about 50° C.

[0080] At the anode compartment outlet, the mixture of gas residues,mainly unburned hydrogen and methane, is recycled towards burner B bymeans of duct 7.

[0081] Burner B is a combustion chamber fed at the top in fuel by duct 7and in air by duct 8. An additional supply of fuel may be planned toensure auxiliary heat. The combustion, when the system is cold, istriggered by means of a plasma produced, for example, by an electricaldischarge between the electrodes of a combustion engine spark plug 9located at the top of burner B. When the temperature of burner B becomeshigh enough, the self-ignition of the combustion occurs and the plasmais no longer necessary.

[0082] In order to increase the efficacy of the heat transfer betweenthe hot gases circulating in burner B and the hydrocarbon to crack inpyrolysis chamber R, metal structures 10, for example of the wing,honeycomb or metal foam type are placed from one end to the other of theburner wall.

[0083] The hot gases resulting from the combustion in the burner escapethrough duct 11 located at the back of burner B. The useful heatcontained in the exhaust gas is recovered in a heat exchanger 12.

[0084] The duration of the pyrolysis sequence is limited by theaccumulation of pulverulent carbon in reactor R. This duration variesaccording to the parameters in the system. It may typically range from15 to 30 minutes. When reactor R is full of carbon, it is necessary topass to the regeneration phase.

[0085] Concerning the regeneration phase, a simple way to eliminate thecarbon accumulated in reactor R consists of oxidising it to form amixture of CO and CO₂. An appropriate and heated flow of air isintroduced through heat exchanger 6 at the top of reactor R by means ofduct 13. Duct 3 is then closed. The reactions of the carbon with theoxygen in the air are:

C+O₂→CO₂

ΔH₂₉₈=−393.51 kJ

C+½O₂→CO

ΔH₂₉₈=−110.53 kJ

C+CO₂→2CO

ΔH₂₉₈=−172.45 kJ

[0086] The CO+CO₂ mixture thereby formed is evacuated by duct 5 and ledto the burner by duct 7. During this regeneration phase, PEM fuel cell 1should not receive CO. For this purpose, it is isolated by means ofelectrovalves 14. It should be noted that electrovalves EV placed on theducts, controlled by an electric control circuit control the differentsupplies of gas. The conversion of CO into CO₂ is achieved by thecombustion of the gases in the burner.

[0087] The heat given off is recovered in heat exchanger 6 beforeadmission in burner B and then the excess heat not transmitted throughthe walls of the burner is recovered by heat exchanger 12 via theexhaust gases.

[0088] If we consider the pyrolysis of methane or propane with thedevice represented in FIG. 1, the ideal reactions are:

CH₄→C+2H₂

ΔH₂₉₈=+74.6 kJ

CH₄→3C+4H₂

ΔH₂₉₈=+103.86 kJ

[0089] The pyrolysis thereby allows for the extraction of a maximum of 2moles of hydrogen per mole of methane and 4 moles of hydrogen per moleof propane.

[0090] As indicated in FIG. 1, the method in the invention, allows forthe co-production of heat and electricity from hydrocarbons such asnatural gas or propane. The heat is recovered by the two exchangers 6and 12. Electricity is here produced by a PEM fuel cell 1 that issupplied by the hydrogen derived from pyrolysis.

[0091] If the yield of the PEM fuel cell is 50%, this device produces amaximum of 241 kJ of electricity per mole of methane, that is 30% of theNCV of methane. The thermal energy that can be recovered on theexchangers is then 247 kJ. In co-generation, the maximum value of theglobal NCV yield of the heat+electricity production is therefore 61%. Inthe case of propane, a production of electricity of 482 kJ is obtainedper mole of propane, that is 23.6% of the NCV of propane. The thermalenergy that can be recovered on the exchangers will be 1180 kJ per moleof propane. The maximum value of the global NCV yield of theheat+electricity production is therefore 81%. This example is given byway of indication in order to define an order of magnitude of the powerproduced and the yields.

[0092]FIG. 2 represents a pyrolysis device according to the inventioncoupled with a high temperature SOFC fuel cell 15. Its function is thento transform the fuel into synthesis gas (CO+H₂) that is directlyuseable by fuel cell 15. This conversion upstream from the cell will becalled pre-reforming.

[0093] It is well known that the conversion yield of SOFC fuel cells isimproved when they are supplied with synthesis gas (CO+H₂) rather thandirectly by a hydrocarbon.

[0094] Besides the benefit represented by the improved yield, anotherbenefit is related to the length of operation of the SOFC fuel cell. Infact, an attempt to avoid the outer reforming would lead to theintroduction of hydrocarbon in the anode compartment of fuel cell 15 andto proceed with the inner vapour-reforming using the water formed at theanode. This very elegant solution however comes up against a majordifficulty linked to the deposit of carbon in fuel cell 15. In fact,pyrolysis reactions of the hydrocarbon can not be avoided at workingtemperatures of SOFC fuel cell. These reactions produce solid carbonthat accumulates in fuel cell 15 where it perturbs the operation. Inorder to avoid this problem, it is advisable to have a pre-reformerupstream from fuel cell 15. In this case, reactor R will play this role.In fact, H₂ is produced during the pyrolysis phase and CO during theregeneration phase. The device presents a great many similarities withthe case presented above for a PEM fuel cell except for the followingpoints:

[0095] Heat exchanger 6 located at outlet 5 is no longer useful sincethe gases derived from the pyrolyser can be introduced at hightemperature in the anode compartment of fuel cell 15.

[0096] Electrovalves 14 were eliminated since fuel cell 15 accepts COand therefore doesn't need to be isolated during the regeneration phase.

[0097] The air flow entering the cathode compartment of fuel cell 15leaves very hot and is recycled in both directions. Electrovalve EV1leads the hot air to burner B through duct 8 to maintain the combustion,or to reactor R through duct 13 for the regeneration sequence.

[0098] The operation of the method during the pyrolysis phase is fairlyidentical to that described in the example in FIG. 1 when the pyrolysersupplies a PEM fuel cell. However, the following differences are noted:

[0099] Fuel cell 15 very well accepts being fed a H₂+CO mixture ofgases. The constraint to produce a gas rich in hydrogen and fully exemptof CO is no longer required in the present situation. It is thereforepossible to expand the choice of fuel to pyrolyse and extend it toethanol or other oxygenised fuels.

[0100] During the pyrolysis phase, a mixture of gas rich in hydrogen isproduced with possibly a CO content. This mixture of gas is extractedfrom reactor R by duct 5 and is directly sent to the anode compartmentof fuel cell 15.

[0101] The gas emissions of fuel cell 15 leave at high temperature andare directed towards burner B by duct 7 to finish combustion. Thiscombustion is provided by an additional supply of very hot air broughtby duct 8 and removed at the outlet of the cathode compartment of fuelcell 15.

[0102] During the regeneration phase, as in the case of coupling with aPEM fuel cell, the pulverulent carbon accumulated in reactor R duringthe pyrolysis sequence should be gasified by oxidation. It should benoted that there is a basic difference here with the case of a PEM fuelcell. In fact, in the present case, the mixture of CO+CO₂ gases producedduring regeneration in reactor R can be directly sent to the anodecompartment of fuel cell 15 via outlet 5. Therefore, due to theconversion of CO in fuel cell 15, an additional contribution to theproduction of electricity is obtained. To maximise this contribution,the operating parameters during the regeneration phase should be set sothat the ratio α=CO/CO₂ resulting from the oxidation of carbon is amaximum.

[0103] The means to maximise this ratio consist of carrying out gentlecombustion of the carbon during the regeneration phase in order to stopthe reaction at the formation of CO, that is mainly:

[0104] to reduce the air supply,

[0105] to reduce the temperature of the reactor,

[0106] to inject water vapour into the reactor.

[0107] By way of example, a. SOFC fuel cell is considered operating withan electrical conversion efficiency of 45% and is supplied with gasesproduced during pyrolysis. The reactor is supplied with methane and thepyrolysis reaction produces full conversion of this fuel. With thehydrogen produced, it turns out that this device provides a maximum of217 kJ of electricity per mole of methane, that is 27% of the NCV ofmethane.

[0108] If the CO produced during the regeneration phase is alsoconverted into electricity, an additional contribution is added to theelectric production of a SOFC fuel cell that may reach 127 kJ ofelectricity per mole of methane, that is 16% of the NCV of methane. Theglobal electric production may thereby in principle reach 344 kJ ofelectricity per mole of methane, that is 43% of the NCV of methane. Theproduction of heat energy is therefore considerably the same.

[0109] A system of co-generation operating with methane according tothis principle can then produce a considerably equal electrical powerand thermal power with a global efficiency (heat+electricity) of about80%.

[0110] The same system supplied with propane, from the hydrogen formed,may reach an electric production of 434 kJ of electricity per mole ofpropane, that is 21% of the NCV of propane. The electric production fromthe CO formed may reach 381 kJ per mole of propane, that is 18.7% of theNCV of propane. The global electric production may thereby in principlereach 815 kJ of electricity per mole of propane, that is 40% of the NCVof propane. Again in this case, the production of thermal energy isconsiderably equal to the electric production and the global efficiency(heat+electricity) reaches about 80%.

[0111] Contrary to most of the results obtained with the solutions knownto date, it should be noted that the electrical and thermal power givenoff are more or less the same.

[0112] The performances announced above assume full pyrolysis andregeneration reactions, which is not the case in reality. It thereforeconsists of maximum values that it is necessary to try to reach in realconditions.

[0113]FIG. 3 represents a system with two reactors R1 and R2 to obtaincontinuous and no longer cyclic operation. The two reactors are definedby an outer cylindrical wall and by the cylindrical walls of burner B′.The reactors, like the burner, are respectively enclosed in a top andbottom in the shape of a spherical cap. The reactor-burner unit isplaced in a cylindrical heat-insulated sheath 16 intended to facilitatethe maintenance of the pyrolysis reactors at high temperature and reducethe heat losses of the system.

[0114] The operating principles of the double pyrolysis chamber deviceare much the same as those described above in reference to FIGS. 1 and2. The existence of two reactors helps one operate in pyrolysis sequencewhile the other operates in regeneration sequence and vice versa. Thismeans that a reactor producing hydrogen-rich gas produced by pyrolysisand a reactor in regeneration sequence providing the oxidation of carbonis constantly available.

[0115] In this diagram, we discern:

[0116] Burner B′: located at the centre of the system. It is cylindricaland has a shell ring at the centre enabling the enlargement of thecombustion chamber. This shell ring helps house ignition device 10 atthe middle of the left side of burner B′ and the passage of severalpipes at the middle of the right side: an evacuation duct 17 collectingthe smoke at the top of burner B′, a duct 18 supplying the burner withfuel at the bottom and a duct 19 supplying the burner with air also atthe bottom.

[0117] A reactor R1 located at the top part of the device and a reactorR2 at the bottom:

[0118] The two reactors R1 and R2 are identical. Both are connected to afuel supply duct 20, an air supply duct 21 and a duct for the evacuationof products 22.

[0119] For reactor R1, ducts 20 and 21 are placed at the top of thereactor and duct 22 at the bottom just above the ducts for burner B. Forreactor R2, ducts 20 and 21 are placed at the bottom of the reactor andduct 22 at the top, just below the ducts for burner B′.

[0120] The transfer of heat between the hot gases (fumes) of burner B′and each reactor is provided by high efficiency heat exchange structures23 of the same type as those mentioned in the examples of FIGS. 1 and 2.

[0121] The carbon particles produced by the pyrolysis reactions aretrapped in reactor R1 and in reactor R2 by filters 24 in refractoryfibres, for example, in aluminium fibres, located in ducts 22, on eachside of the right side of the shell ring.

[0122] This double reactor system can be used to constantly supply a PEMfuel cell connected in an analogous manner to the case represented inFIG. 1 or a SOFC fuel cell connected in an analogous manner to the caserepresented in FIG. 2.

[0123]FIG. 4 represents a full circuit incorporating the device in FIG.3. Here, only the gas supply circuits comprising electrovalvescontrolled by an electrical control circuit will be described.

[0124] The supply of pyrolysis chambers (R1, R2) occurs by means of twosupply circuits:

[0125] on for the fuel. It comprises a 3 track valve EV2 in turndelivering in both reactors,

[0126] the other for the air. It comprises a 3 track valve EV3 in turndelivering in both reactors and piloted by the control circuit so as toinject air in the reactor that is not supplied with fuel in order toprovoke the combustion of pulverulent carbon derived from the pyrolysisreaction carried out during the previous cycle.

[0127] Both outlet ducts for the gases from the reactors convergetowards a set of two 3 track electrovalves, EV4 and EV5, that can sendthe gases produced during the pyrolysis and during the partialcombustion of the carbon, in the fuel cell for electrovalve EV4 and inthe burner for electrovalve EV5.

[0128] The burner is supplied in air by the same supply circuit as thepyrolysis chambers but upstream from electrovalve EV3 and in fuel viaeither electrovalve EV5 as described supra or electrovalve EV6controlling the choice of gases derived from the fuel cell or the fuelby an engagement upstream from electrovalve EV2.

[0129]FIGS. 5, 6 and 7 describe a variant of the device, the object ofthe invention, consisting of incorporating, before the fuel cell, ahydrogen purification membrane in the circuit for the extraction ofgases produced by the pyrolysis. The system can thereby be used as avery pure hydrogen generator.

[0130] There are two categories of hydrogen permeable membranes that maybe used in the system:

[0131] polymer membranes. They are very extensively used for thepurification of hydrogen in industry. Such membranes only operate at lowtemperature, less than 120° C., and can therefore only be used outsideof the reactor, after the cooling of the hydrogen-rich gas (FIG. 5),

[0132] metal membranes. They are very selective membranes consisting ofa very hydrogen permeable metal, generally an alloy of palladium. Thesemembranes can be used at high temperature, typically 500 to 550° C. Theycan therefore be integrated either in the high temperature gas circuit(FIG. 6) or in the reactor strictly speaking (FIG. 7).

[0133]FIG. 5 represents a device using a polymer membrane 25. The deviceis similar to that in FIG. 1 except for the following points:

[0134] Membrane 25 is sandwiched between heat exchanger 6 and the fuelcell;

[0135] The mixture of hydrogen-rich gas extracted from the reactor byduct 5, then cooled at under 120° C. by means of exchanger 6 is sent tothe purifier at membrane 25. It leaves by two channels. The firstchannel V1 carries the very pure hydrogen thereby extracted to the PEMfuel cell in order to supply it and the second channel V2 evacuates theresidual gases that are recompressed with a heating compressor 26 so asto be recycled with the fuel supplying the pyrolysis reactor by duct 3.

[0136]FIG. 6 represents a device using a metal membrane 27 made ofpalladium alloy operating at high temperature. This device is similar tothat in FIG. 4 except for the fact that membrane purifier 27 is locatedin front of heat exchanger 6. The very pure hydrogen thereby extractedis sent towards the PEM fuel cell after being cooled by means of heatexchanger 6. The residual gases are recompressed by means of compressor26 in order to be recycled with the fuel supplying the pyrolysis reactorby duct 3.

[0137]FIG. 7 represents a device presenting a metal membrane 28 placedinside the pyrolysis reactor. This membrane made of palladium alloyoperates at high temperature, typically at 500-550° C. and has the shapeof a cylindrical rod. In order to avoid an accumulation of carbonparticles in direct contact with the membrane, the latter is protectedby a sleeve 29 of refractory fibres, for example an aluminium fabric.The purpose of this sleeve is to keep the carbon particles away from themembrane.

[0138] It should be noted that pyrolysis reactor R can contain, ifnecessary, several identical membranes so as to increase the activemembrane surface and thereby the flow of hydrogen extracted.

[0139] It should also be noted that even if a membrane consisting of acylindrical pencil or a beam of cylindrical rods is one of thepossibilities considered, other configurations are also possible.Therefore, membranes in the form of plates or a stack of plates can alsobe considered.

[0140] The main advantage of placing the membrane inside the pyrolysisreactor is the simplicity of the system since compressor 26 and the fuelcirculation loop are not required.

[0141] The devices represented in FIGS. 5 to 7 can be adapted to thecase of the double pyrolysis reactor in FIG. 3. This adaptation does notraise any specific problems.

[0142] Among the applications of the method, we can include theproduction of co-generation boilers (heat and electricity) in thehabitat sector as well as recreational vehicles (camping cars, trailers,. . . ). For home applications, for example single family homes, thepower level of a co-generation module will be about 5 kWe+5 kWth.

[0143] According to the case, the fuels are: natural gas, propane,domestic fuel, . . .

[0144] In particular PEM and SOFC fuel cells offer plans adapted to thistype of application.

[0145] For more powerful installations, such as the urban co-generationfor buildings, groups of buildings, hospitals, modules with a power ofabout 200 kWe+200 kWth have to be developed. Considering the relativelylow cost and very developed distribution, natural gas will be the fuelmost often used for this application.

[0146] Openings in the field of farm applications are also to beconsidered. For example, farm greenhouses reveal the need for heat andelectricity. It should be possible to use ecological fuels such asethanol for such applications.

[0147] An application of the method has a place in the petrochemicalsfield. In fact, the method is an easy and cheap way to produce synthesisgas (CO+H₂) for which there are major uses in the chemistry industry(manufacture of acetic acid, formic acid, acrylic acid, phosgen,isocyannates, . . . ).

1. Method for the production of a hydrogen-rich gas that can be used ina fuel cell, by thermal pyrolysis of hydrocarbons, consisting ofcarrying out, in a reactor thermal cracking, without catalyst, topyrolyse a fuel chosen so as to produce either a gas rich in hydrogenfree of carbon monoxide, or a gas rich in hydrogen containing hydrogenmonoxide, and to use the gas emissions produced during the pyrolysis andinert with respect to the cell as a fuel in the burner to ensure heatingof the reactor in order to bring it to the reaction temperature. 2.Method according to claim 1, wherein the pulverulent carbon produced insaid reactor during the pyrolysis reaction is collected for industrialuse.
 3. Method according to claim 1, wherein the pulverulent carbonproduced in said reactor during the pyrolysis reaction is burned so asto produce carbon monoxide, at least in part, or to produce carbondioxide (heat) to complete the heating of the reactions and possiblyensure a connected system of heating.
 4. Method according to claim 1,wherein the reactor comprises at least one pyrolysis chamber.
 5. Methodaccording to claim 1, wherein the reactor comprises at least twopyrolysis chambers unused in turn, the unused chamber being regeneratedby introduction of air that induces the combustion of the carbondeposited during the pyrolysis phase.
 6. Method according to claim 1,wherein the reactions are triggered and maintained by the heat providedby the combustion reaction of the carbon by a burner.
 7. Methodaccording to claim 6, wherein said burner is located at the centre ofthe pyrolysis chambers.
 8. Method according to claim 6, wherein saidburner is supplied by an air/fuel mixture that is ignited by a sparkcreated between the two electrodes of a spark plug.
 9. Method accordingto claim 8, wherein said burner, once the reactions are triggered, issupplied by the gas leaving the fuel cell and/or the carbon monoxidecontained in the gas produced during the co-generation.
 10. Methodaccording to claim 4, wherein the heat transfer between the burner andsaid pyrolysis chamber is ensured by a specific structure.
 11. Methodaccording to claim 10, wherein said structure is metallic.
 12. Methodaccording to claim 10, wherein said structure is in the form of wings,honeycomb, foam.
 13. Method according to claim 10, wherein saidstructure is arranged on the inner and outer walls of the burner. 14.Method according to claim 1, wherein said reactor contains a filterpreventing the carbon from leaving the reactor and penetrating in thefuel cell.
 15. Method according to claim 14, wherein said filterconsists of a porous fire-proof material.
 16. Method according to claim14, wherein said filter consists of a layer of aluminium wool. 17.Method according to claim 1, wherein the hydrogen is extracted andpurified by means of a permeable hydrogen-selective membrane.
 18. Methodaccording to claim 17, wherein the membrane is a polymer membrane. 19.Method according to claim 17, wherein the membrane is a metallicmembrane.
 20. Method according to claim 1, wherein the pyrolysisreaction is activated by means of a plasma generator incorporated in thereactor.
 21. Method according to claim 20, wherein the plasma generatoris a <<barrier>> discharge generator.
 22. Method according to claim 20,wherein the plasma generator is a microwave discharge generator. 23.Device for the production of a hydrogen-rich gas that can be used in afuel cell, by thermal pyrolysis of hydrocarbons according to a methodconsisting of, in a reactor, carrying out thermal cracking, without acatalyst, to pyrolyse a fuel chosen so as to produce either a gas richin hydrogen free of carbon monoxide, or a gas rich in hydrogencontaining carbon monoxide, and to use the gases emitted during thepyrolysis and inert with respect to the cell as fuel in the burner toensure the heating of the reactor in view of bringing it to the reactiontemperature, comprising at least one reactor surrounding a burner andmeans enabling the alternative operation in pyrolysis sequence andre-generation sequence.
 24. Device according to claim 23, wherein thenumber of reactors is variable and of different forms.
 25. Deviceaccording to claim 23, wherein reactor is defined by the cylindricalwall of the burner and an outer coaxial cylindrical wall of the burner,reactor being enclosed by a spherical cup-shaped bottom and by aring-shaped top located around the top of the burner; the reactor-burnerunit is placed in a heat insulated sheath.
 26. Device according to claim23, wherein the two reactors are defined by an outer cylinder and by thecylindrical wall of the burner; the reactors as well as the burner areenclosed by a spherical cap-shaped top and bottom; the reactor-burnerunit is placed in a heat insulated sheath.
 27. Device according to claim26, wherein burner has a shell ring in the middle.
 28. Device accordingto claim 23, comprising the means to recover the non consumed thermalpower.
 29. Device according to claim 28, wherein said means are heatexchangers.
 30. Device according to claim 23, comprising electrovalvesthat ensure the management of the different gas flows.
 31. Deviceaccording to claim 30, wherein said electrovalves are located on thedifferent air and fuel supply ducts.
 32. Device according to claim 30,wherein said electrovalves are located on the pyrolysis chamber outletducts.
 33. Device according to claim 30, wherein said electrovalves arelocated on the fuel cell inlets.